1. Field of the Invention
This invention relates to a photocurable composition and this is photosensitive capsules, used in image forming apparatus or printers.
2. Description of the Related Art
Photosensitive capsules which internally hold image forming materials such as dye precursors, dyes, pigments or the like and respond to light to cause a change in mechanical strength are known in the art as disclosed in Japanese Patent Application Laid-open No. 5-066559. Image forming apparatus which employ toners comprised of such photosensitive capsules are also disclosed in Japanese Patent Applications Laid-open No.5-068871, No.5-066559 and No. 5-297552, in which the toners are exposed to light and thereafter images are formed on image-receiving paper by a developing process that applies, e.g., a pressure to break only toner capsules having lower strength.
In the photosensitive capsules used in such image forming apparatus, photocurable compositions containing a dye material or the like are used. As photocurable compositions containing no dye material, various ones are known for a long time. For example, a photoradically polymerizable composition is formed of a radically polymerizable unsaturated group-containing compound as a base material, a photopolymerization initiator, a sensitizer and so forth added thereto.
In this instance, the photopolymerization initiator includes benzil, Michler's ketone, diethyl thioxanthone, benzophenone and acetophenone, which are each used alone.
As composite type photopolymerization initiators, they are known to include as follows:
(1) a composite type initiator comprised of a dye and an aliphatic amine (Japanese Patent Publication No.44-20189); PA1 (2) a composite type initiator comprised of a hexaarylbiimidazole, a radical generator and a dye (Japanese Patent Publication No. 45-37377); PA1 (3) a composite type initiator comprised of a hexaarylbiimidazole and a p-dialkylaminobenzilidene ketone (Japanese Patent Application Laid-open No. 47-2528); PA1 (4) a composite type initiator comprised of a cyclic cis-.alpha.-dicarbonyl compound and a dye (Japanese Patent Application Laid-open No. 48-84183); PA1 (5) a composite type initiator comprised of a carbonyl compound and a tertiary amine (Japanese Patent Application Laid-open No. 52-134692); PA1 (6) a composite type initiator comprised of a substituted triazine and a merocyanine dye (Japanese Patent Application Laid-open No. 54-151024); PA1 (7) a composite type initiator comprised of biimidazole and indanone (Japanese Patent Application Laid-open No. 54-155292); PA1 (8) a composite type initiator comprised of a hexaarylbiimidazole and a p-dialkylaminostilbene derivative (Japanese Patent Application Laid-open No. 57-21401); PA1 (9) a composite type initiator comprised of a hexaarylbiimidazole and a p-alkylaminocinnamylidene derivative (Japanese Patent Application Laid-open No. 58-19315); PA1 (10) a composite type initiator comprised of a triazine derivative and a cyanine dye (Japanese Patent Application Laid-open No.58-29803); PA1 (11) a composite type initiator comprised of a triazine derivative and a thiapyrylium salt (Japanese Patent Application Laid-open No. 58-40302); PA1 (12) a composite type initiator comprised of a hexaarylbiimidazole and an n-dialkylaminostilbene derivative, or of a p-dialkylaminophenylbutadienyl derivative and a thiol compound (Japanese Patent Application Laid-open No. 59-56403); PA1 (13) a composite type initiator comprised of a ketone substituted derivative and an organic peroxide (Japanese Patent Application Laid-open No. 60-32801); PA1 (14) a composite type initiator comprised of an .alpha.-diketone and a mercaptocarboxylic acid (Japanese Patent Application Laid-open No. 61-258802); and PA1 (15) a composite type initiator comprised of an .alpha.-diketone and a polysulfide (Japanese Patent Application Laid-open No. 61-258803). PA1 the aniline compound is at least one of 2,6-diisopropyl-N,N-dimethylaniline and 2,4,6,N,N-pentamethylaniline. PA1 said aniline compound is at least one of 2,6-diisopropyl-N,N-dimethylaniline and 2,4,6,N,N-pentamethylaniline, and said dye is at least one of a coumarin dye and a cyanine dye. PA1 the aniline compound is at least one of 2,6-diisopropyl-N,N-dimethylaniline and 2,4,6,N,N-pentamethylaniline.
However, photocurable compositions making use of any of these photopolymerization initiators of a sole type or composite type have a problem that a photocuring sensitivity is poor and a curing velocity is low and hence time longer than intended is required in order to record images.